PIGMENTATION IN OLD AMERICANS HRDLICKA. 449 



disappeared from the eyes, nearly disappeared from the skin, and 

 was greatly diminished in the hair. The result so far as the visual 

 organ was concerned was the blue eye, which became fixed by heredity. 

 The blue eye, as already noted, is not an eye wholly without pigment — 

 that condition is present only in the eye of the full albino; neither 

 is it an eye with any special pigment. But whatever pigment is 

 present in the blue eye is located only in the posterior columnar 

 epithelium cells of the iris, whereas in gray, brown, and the so-called 

 black eyes pigment is found also in branching connective tissue cells 

 interspersed between the bundles of connective tissue that form the 

 substance or stroma of the iris, and even in the endothelial cells on the 

 front of the iris. 



If an unmixed blue-eyed person marries one with brown eyes, the 

 result, as shown in the color of the eyes of the progeny, may be one 

 of several distinct conditions. In a small number of cases of such 

 progeny, taken at large, it will be seen that the brown pigment owed 

 to the darker mate has been distributed uniformly throughout the 

 iris, and, according to its quantity, instead of a blue eye we shall have 

 " grays," possibly some " greens," and light browns, the latter of which 

 in a strong light may show a greenish tinge. But in the large ma- 

 jority of cases the distribution of the brown pigment in the iris will 

 be more or less localized, and we shall have a bluish (never perfectly 

 blue), grayish, or greenish eye with a brown ring or area about the 

 pupil, or brown specks or spots scattered over the iris, with a closer 

 aggregation about the pupil. These cases constitute the large cate- 

 gory of " mixed " eyes which are encountered in the central and north 

 European peoples of the present time, and which are very common 

 among Americans. 



CLASSIFICATION. 



A detailed investigation on pigmentation in a highly complex popu- 

 lation, such as that of the United States, offers, due to the conditions 

 enumerated above, some difficulties. There are a large number of 

 shades in the color of the skin and hair which pass into each other 

 without any lines of demarcation, and in the case of the eyes there 

 are numerous mixtures that are not always easy of characterization. 

 A correct appreciation and recording of the true conditions requires 

 good eyesight in the observer, proper light, distance, and exposure 

 (skin) in examination, a careful effort at distinguishing the true 

 conditions, and the simplest possible thoroughly understood scheme 

 of classification. Fortunately extreme details, except in some special 

 researches, are not necessary, and the many shades met with may 

 be grouped into a few categories that are not only sufficient for 

 ordinary scientific purposes, but are also readily intelligible to the 

 nonscientific man. 



